There is very little information regarding the degree of sexual differentiation in the central nervous system control of gonadotropin secretion in primates. The information that does exist indicates that the primate brain is less sexually different than is the brain of non-primates. Our goal in this funding period is to investigate the degree to which the central nervous system is sexually differentiated in the control of gonadotropin secretion in rhesus monkeys. Gonadotropins, and in particular, LH (luteinizing hormone), are secreted from the pituitary in discrete pulses. It is generally accepted that the stimulus for these pulses of LH is the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Therefore, a change in frequency of LH pulses would indicate a change in the frequency of GnRH release. It has also been established that gonadal steriods can dramatically influence the frequency of pulsatile LH secretion, which differs between males and females. Since the brain in the male is exposed to a different steroid environment (testosterone) than is the brain of the female (estradiol and progesterone), the question arises as to where does the control for the pulsatile secretion of LH exist, in the brain or in the gonad? We have developed a model in which we can expose the brain of the differentiated sex (male) to the physiologic secretions of both gonads. We plan to analyze the frequency of pulsatile LH secretion in intact male rhesus monkeys, then castrate those monkeys and transplant an ovary from a female rhesus monkey into each of the castrated males and then analyze the LH pulse frequency in these transplanted males. From this information we should be able to determine if the male brain alters the LH pulse frequency in response to physiologic ovarian stimulation. A better understanding of the control of the secretion of reproductive hormones will eventually lead to more effective regulation of fertility.